Objectives: To assess the relevance of maximal
inspiratory flow rates (MIFR) in the assessment of airway obstruction
Setting: University teaching hospital.
Participants: Ten consecutive COPD patients (O group; mean[±
SD] age, 58.5 ± 8.3 years) and 10 matched healthy subjects (H
group; mean age, 58.7 ± 7.4 years).
Lung volumes, FEV1, specific airway conductance,
single-breath lung diffusing capacity, MIFR, and maximal expiratory
flow rates (MEFR).
FEV1/vital capacity (VC) was 74.7% in the H group and
37.8% in the O group (p < 0.001). Total lung capacity was higher
(p < 0.001) in the O group compared with the H group. Lung diffusing
capacity was less than half in the O group compared with the H group
(p < 0.001). MEFR at all lung volumes were lower in the O group
(p < 0.001). MIFR were comparable in the two groups, except at 25%
inspired VC, where MIFR were lower in the O group (p < 0.05).
Conclusion: MIFR are less sensitive than MEFR to detect
airway obstruction in COPD patients. Yet, the interest of MIFR lay in
the possibility to separate intrinsic from extrinsic involvement of
airways. A normal MIFR associated with low MEFR, as in the present
study, suggests either a lack of parenchymal support, an increased
collapsibility of the airways, or a reversible peripheral airway
narrowing. A fixed, generalized airway narrowing would be associated
with a decrease of both MIFR and MEFR.